High-spin rotational bands in123I

Abstract

High-spin states in 123 I were populated in the reaction 80 Se( 48 Ca,p4n) 123 I at a beam energy of 207 MeV and γ -ray coincidence events were measured using the Gammasphere spectrometer. Three weakly populated, high-spin rotational bands have been discovered with characteristics similar to those of the long collective bands recently observed in other nuclei of this mass region. Configuration assignments are proposed based on calculations within the framework of the cranked Nilsson-Strutinsky approach.The nuclei in the A = 125 mass region, with a limited number of valence nucleons outside the 114 Sn core, undergo a transition from weakly prolate deformation at low spin to an oblate shape at medium spin. The shape change is induced by the successive alignment of nucleons along the rotation axis and, finally, the level sequences terminate in maximally aligned oblate states [1][2][3][4][5][6]. In addition, several high-spin rotational bands have recently been observed in 120 Te [7], 124 Ba [6], 125 I [8], 125 Xe [9], and 126 Xe [10], which extend far beyond the noncollective oblate states. Only some of these sequences are firmly connected to lower-lying levels; they feed normal-deformed states in the spin range of I 25 at excitation energies around 10 MeV.In the present work, the results of a further analysis of the data from the experiment to investigate the high-spin structure of 123 I [2] are reported. This investigation revealed three highly deformed bands in this nucleus. Their properties are similar to those of the long bands observed in neighboring nuclei. Cranked Nilsson-Strutinsky (CNS) calculations have been employed to propose configurations for the new bands.High-spin states in 123 I were populated using the reaction 80 Se( 48 Ca,p4n) 123 I. The beam with an energy of 207 MeV was provided by the ATLAS accelerator at ANL. The target consisted of a 80 Se layer with a thickness of 0.6 mg/cm 2 . Gamma-ray coincidence events were recorded with the Gammasphere spectrometer [11]. Further details on the experiment and the data analysis are given in previous publications by the present collaboration [2,7].The three rotational sequences with large moments of inertia discovered in 123 I are displayed in Fig. 1. Their intensities are <1% of the channel strength. Bands a and b are about equal in intensity, while band c is weaker. Such small intensities preclude a measurement of directional correlations. However, the regularity of the bands and their similarity with high-spin bands in neighboring nuclei suggests that the in-band transitions are of E2 multipolarity. It was not possible to establish linking transitions into known 123 I levels. Excitation energies and spins of the new bands were estimated on the basis of the observed coincidences. These values were varied within reasonable limits to give agreement with theoretical predictions for the suggested configurations. The adopted values are similar to those of the connected bands in the neighboring nuclei 125 I [8], 125 Xe [9], and 126 Xe [10].Triple-gated γ -ra...

Collective and noncollective excitations in122Te

“…The seven unconnected high-spin bands exhibit features similar to those of the long collective bands discovered recently in several nuclei of the region with neutron numbers between N = 68 and 72 [10,12,[15][16][17][18]. Configurations for the new high-spin structures are suggested on the basis of comparisons with the results of CNS calculations.…”

“…In several recent studies, high-spin rotational bands with large deformation were observed in nuclei with neutron number N = 68-72; i.e., in 120 Te [10], 123 I [12], 125 I [16], 125 Xe, [17], 126 Xe [18], and 124 Ba [15]. Some of these sequences extend into the spin-60 region.…”

“…The seven new high-spin rotational bands in 122 Te exhibit features similar to the long collective bands in neighboring nuclei with neutron numbers N between 68 and 72 [10,12,[15][16][17][18]. Since these new bands are not linked to the lower-lying states of the level scheme, configuration assignments based on comparisons with CNS calculations can only be viewed as tentative.…”

“…For the nuclei in this mass region with a small number of particles outside the 114 Sn core, the total angular momentum obtained by coupling the individual spins of all valence particles is limited. Recently, maximally aligned states with 8 to 11 particles were observed [10][11][12][13]. Moreover, states with one or two particles antialigned with respect to the rotation axis of the other valence particles were discovered in 120 Te [10] and 123,125 I [11,12].…”

“…Recently, maximally aligned states with 8 to 11 particles were observed [10][11][12][13]. Moreover, states with one or two particles antialigned with respect to the rotation axis of the other valence particles were discovered in 120 Te [10] and 123,125 I [11,12]. In 121 I [13], 123 I [12], 123 Cs [14], and 124 Ba [15], low-intensity, high-energy γ -ray transitions were found to feed the maximally aligned states.…”